1. Field of the Invention
The present invention concerns clutch cover assemblies, for automobile vehicles in particular, of the type comprising a pressure plate equipped with axial retaining means.
2. Description of the Prior Art
As is well known, a clutch cover assembly principally comprises a cover, an engagement member such as a diaphragm spring and at least one pressure plate. The cover, generally hollow, comprises an annular back, a skirt with openings and a flange for fixing the cover to a reaction plate, also called the flywheel, which is generally fastened to a driving shaft, the internal combustion engine output shaft in the case of an automobile vehicle, for example. The pressure plate is designed to be urged away from the back of the cover by the engagement member so as to press on a friction disk fast with a driven shaft and disposed axially between the pressure and reaction plates.
To this end the pressure plate is rotationally coupled to the cover, with provision for relative axial movement between them.
In practice the link between the cover and the pressure plate is provided by axially flexible circumferential strips the respective ends of which are fixed to radially projecting tabs formed on the pressure plate and fixing lugs fast with the cover. The tabs on the pressure plate pass through the skirt of the cover by means of the aforementioned openings and the fixing lugs are disposed in the vicinity of these openings.
A distinction is drawn between two major categories of clutch cover assemblies, according to whether they are adapted to be driven by a motor in one particular direction around their axes or whether they are adapted to be associated with motors turning in either direction.
When both directions are possible, the openings in the cover provide for a substantially diametral plane of symmetry, the openings being bordered in the circumferential direction by two fixing lugs disposed in a common transverse plane, designed for fastening the strips for respective directions of rotation.
A symmetrical configuration of the openings corresponds to relatively large overall dimensions axially, radially and circumferentially. Furthermore, for a number of years there has been an increasingly marked preference for one particular direction of rotation (called the forward direction), to the detriment of the other (the reverse or retrograde direction). Thus there have recently been proposed covers with assymetric openings featuring, inter alia, smaller overall dimensions.
The circumferential strips linking pressure plate and cover are in practice critical to the correct functioning of a clutch cover assembly. These are thin parts, of more or less marked curvature according to the position of the pressure plate relative to the back of the cover, the mechanical specifications of which, in particular with regard to their elasticity, must be such that these strips exert on the pressure plate an axial return force towards the back of the cover which is sufficiently low as not to impede the engagement member (more often than not a diaphragm spring) pressing the pressure plate away from the back of the cover so as to drive through friction, under good conditions, a disk of the aforementioned type, but which is also sufficiently high to provide for the lifting of the pressure plate away from the friction disk when the engagement member releases its pressure on said plate.
To preserve the elastic properties of the strips it is necessary to maintain the axial offsetting of their ends, and thus their curvature, within closely specified limits. In particular, during storage, at which time the cover is not fastened to any reaction plate, it is necessary to avoid the pressure plate being moved away from the back of the cover by the engagement member to the point where it causes unwanted plastic deformation of the strips, as a result of which they become warped.
There have been proposed, as shown for example by French Pat. Nos. 2,342,427 and 2,437,525, covers for clutch cover assemblies with only one rotation direction in which the openings are bordered circumferentially by two lugs offset axially (and circumferentially); the lug which is disposed near the back of the cover is called the fixing lug, while the other lug is called the retaining lug. The latter is intended to serve as a bearing member for the axial retaining means carried by the tabs of the pressure plate so as to prevent excessive displacement of the latter relative to the back of the cover. These retaining means comprise, in the case of the aforementioned patents, for example, a circumferential projection on the strips or a bearing surface formed on the tabs themselves.
These axial retaining means thus necessitate specific adaptations to the cover, the pressure plate or the circumferential links, which are either large or delicate parts; also, these axial retaining means more often than not require conjoint and compatible adaptations of two of the aforementioned parts; the axial position of the retaining lugs on the cover must be very precisely defined, for example. These various factors currently entail a multiplicity of manufacturing ranges and storage problems given the various compatible designs of covers, pressure plates and strips to be provised for.
An object of the invention is to alleviate these disadvantages by providing for enhanced standardisation of the aforementioned parts whilst ensuring good protection of the strips. In accordance with the invention, the axial retaining means are formed on a part which is already present in conventional clutch cover assemblies but which is distinct from the cover, the pressure plate or plates and the circumferential strips: thus the invention does not require these latter items to be "compatible" in the sense explained hereinabove.